Resin-impregnated boron nitride sintered body and use for same

ABSTRACT

A resin-impregnated boron nitride sintered body having superior thermal conductivity and superior strength, and a resin-impregnated boron nitride sintered body having superior conductivity and small anisotropy of thermal conductivity are provided. A resin-impregnated boron nitride sintered body, including: 30 to 90 volume % of a boron nitride sintered body having boron nitride particles bonded three-dimensionally; and 10 to 70 volume % of a resin; wherein the boron nitride sintered body has a porosity of 10 to 70%; the boron nitride particles of the boron nitride sintered body has an average long diameter of 10 μm or more; the boron nitride sintered body has a graphitization index by powder X-ray diffractometry is 4.0 or less; and an orientation degree of the boron nitride particles of the boron nitride sintered body by I.O.P is 0.01 to 0.05 or 20 to 100; and a resin-impregnated boron nitride sintered body, including: 30 to 90 volume % of a boron nitride sintered body having boron nitride particles bonded three-dimensionally is provided.

TECHNICAL FIELD

The present invention is related to a resin-impregnated boron nitridesintered body.

BACKGROUND

Regarding exothermic electronic parts such as power devices, double-sideheat dissipation transistors, thyristors, CPU and the like, efficientheat dissipation during their use is important. Generally, conventionalmeasures for such heat dissipation were to (1) improve thermalconductivity of the insulating layer of a printed-wiring board ontowhich the exothermic electronic parts are to be mounted, and (2) mountthe exothermic electronic parts or the printed-wiring board having theexothermic electronic parts mounted thereon onto a heat sink via athermal interface materials having electric insulation or a ceramicsinsulating plate. As the insulating layer of the printed-wiring boardand the thermal interface materials, heat dissipating member obtained bycuring silicone resin and epoxy resin added with ceramics powder isused.

In recent years, higher speed and higher integration of the circuit inthe exothermic electronic parts and higher density of the exothermicelectronic parts being mounted onto the printed-wiring board have leadto higher heat generation density and more precise structure in theelectronic devices. Accordingly, heat dissipating member having evenhigher thermal conductivity has been required.

From the afore-mentioned circumstances, hexagonal boron nitride havingsuperior properties as the electric insulating materials such as (1)high thermal conductivity, (2) high electric insulating property and thelike have been receiving attention. However, while the thermalconductivity of boron nitride is 100 to 400 W/(m·K) in the in-planedirection (direction in the a-axis), the thermal conductivity in thethickness direction (direction in the c-axis) is 2 W/(m·K). Accordingly,anisotropy of the thermal conductivity derived from the crystallinestructure and the flake shape is large. Accordingly, for example, whenthe thermal interface materials is manufactured, the in-plane direction(direction in the a-axis) of the boron nitride particle and thethickness direction of the thermal interface materials can come verticalwith each other, thereby resulting in cases where the high thermalconductivity of the boron nitride in the in-plane direction (directionin the a-axis) could not be utilized sufficiently.

(First Viewpoint)

High thermal conductivity of the boron nitride particles in the in-planedirection (direction in the a-axis) can be achieved by allowing thein-plane direction (direction in the a axis) of the boron nitrideparticles and the thickness direction of the thermal interface materialsto come in parallel with each other, however, there is a problem in thatthe material is weak in the tensile stress in the thickness direction.

In Patent Literature 1, a resin composite material containing highrigidity particles such as ceramics and metals by 40 to 90% by volumefraction, the high rigidity particles being in contact with each otherthree-dimensionally, and a manufacturing method thereof are disclosed.Here, it is also disclosed that such resin composite material can besuitably used in mechanical parts such as a slide member exemplified asa wire saw roller and a gear wheel.

In addition, Patent Literature 2 discloses a sintered ceramics memberhaving at least forsterite and boron nitride as its main component andhaving boron nitride aligned in one direction, a probe holder formed byusing the ceramics member, and a manufacturing method of the ceramicsmember. Here, it is also disclosed that such ceramics member can besuitably used as a material for a probe holder, into which a probe isinserted. Here, the probe is for a micro contactor used in inspection ofsemiconductors and liquid crystals, and electrically connects a circuitstructure to be inspected and a circuit structure which output signalsfor inspection.

Patent Literature 3 discloses a method in which a filler having a largeanisotropy in shape or in thermal conductivity is mixed and dispersed ina thermosetting resin material, followed by curing of the thermosettingresin. Subsequently, the cured thermosetting resin is crushed, mixedwith a thermoplastic resin to obtain a resin composition for a mold, andthen the resin composition is heated to soften and mold the resincomposition into a desired shape.

Patent Literatures 4 and 5 disclose of a method for manufacturing asubstrate for a printed circuit comprising the step of impregnating athermal setting resin (II) into an inorganic continuous porous bodyselected from the group consisting of an aluminum nitride-boron nitridecomposite (AIN—BN), an alumina-boron nitride composite (Al₂O₃—BN), azirconium oxide-boron nitride composite (ZrO₂—BN), silicon nitride-boronnitride composite (Si₃N₄—BN), hexagonal boron nitride (h-BN),β-wollastonite (β-CaSiO₃), mica, and volcanic soil; followed by curingto obtain a cured plate body. In addition, it is also disclosed thatsuch substrate for a printed circuit can be suitably used as a substratefor high frequency usage and for directly mounting a semiconductor chip.

Patent Literature 6 discloses a porous body of B—C—N system having agraphite three-dimensional skeletal structure synthesized from a porouspolyimide sheet as a starting material, and a heat dissipating materialobtained by impregnating a resin in the porous portion to obtain acomposite material. Such heat dissipating material has a smaller heatresistance compared with those obtained by impregnating a resin in anordinary carbon porous body, and an insulating composite material can beobtained by the conversion of the porous body into h-BN. Accordingly,the heat dissipating material is a promising material as a coolingmaterial for electronic parts which require low heat resistance andelectric insulating property.

(Second Viewpoint)

In addition, not only the heat dissipation in one direction of thethickness direction or the plane direction as conventionally required,but also high heat dissipation in both of the thickness direction andthe plane direction is required.

Patent Literature 7 discloses a substrate for an electronic circuitcomprising a ceramics composite obtained by filling a resin in openpores of a porous ceramics sintered body, the porous ceramics sinteredbody having a three-dimensional network crystalline structure. Here, theporous ceramics sintered body is structured with a ceramics material ofwhich crystal grains have an average crystalline grain diameter of 10 μmor less. However, it is difficult to align the flake-like boron nitrideparticles randomly with the method of Patent Literature 7. Accordingly,anisotropy of thermal conductivity could not be decreased.

When the method of Patent Literature 2 was used, the orientation degreeof the flake-like boron nitride was large, showing I.O.P (The Index ofOrientation Performance) of 0.07 or lower. Accordingly, the anisotropyof thermal conductivity could not be decreased.

In the method of Patent Literature 3, thermal conductivity was low asshowing a maximum value of 5.8 W/(m·K). In addition, the thermosettingresin needs to be crushed after being obtained, and then thethermosetting resin is mixed and softened again. Accordingly, it wasproblematic in the viewpoint of reliability due to the possibility ofcontamination and uniformity of the softening condition of the resin.

Patent Literature 8 discloses of increasing the temperature of the moldwhen the resin molding is performed, thereby making random the directionof heat dissipation of the inorganic filler. However, in the method ofPatent Literature 8, alignment of the inorganic filler can be controlledonly insufficiently, and thus the decrease in the anisotropy of thethermal conductivity was insufficient.

Patent Literature 9 discloses of a method in which the manufacturingconditions of the boron nitride is adjusted to allow the flake-likeboron nitride to aggregate, thereby obtaining a pinecone-like boronnitride powder. However, in the method of Patent Literature 9, thepinecone-like aggregated particles of the boron nitride would partlyalign during the coating process and the heat-pressing process performedin the processes to manufacture a thermoconductive sheet, and thus thedecrease in the anisotropy of the thermal conductivity was insufficient.

Patent Literature 10 discloses of impregnating a ceramics powder slurryin a boron nitride sintered body and a composite sintered body, therebyachieving dust free properties. However, since the boron nitridesintered body and the composite sintered body of Patent Literature 10are manufactured generally by powder molding or hot press, alignment ofboron nitride cannot be avoided, and thus there was anisotropy in thethermal conductivity.

Patent Literature 11 discloses a thermoconductive sheet comprisingplate-like boron nitride particles and an organic polymer compoundhaving a glass transition temperature (Tg) of 50° C. or lower; theplate-like boron nitride particles being aligned in the direction oflongitudinal axis thereof with respect to the thickness direction of thesheet. Here, regarding the thermoconductive sheet obtained by the methodof Patent Literature 11, although the thermal conductivity of thethermoconductive sheet in the thickness direction is as high as 26.9W/(mK) at maximum, the plate-like boron nitride particles are aligned,and thus there was anisotropy in the thermal conductivity.

In the conventional technique, the heat dissipating member ismanufactured via a mixing process to mix the ceramics powder such asboron nitride and the resin, an extrusion molding process, a coatingprocess, a heating process and the like. Therefore, it is difficult toavoid the alignment of the boron nitride crystals. Accordingly, thedecrease in the thermal conductivity was limited. The issue of alignmentcan be suppressed when spherical particles of aluminum oxide powders andsilicon oxide powders are used, however, thermal conductivity of theseceramics powders is approximately 20 to 30 W/(m·K) and is lower thanthat of boron nitride. In addition, since the particles are hard, therewas a problem in that the apparatus and the mold would be worn down.Further, in the heat dissipating member manufactured by conventionaltechnique, thermoconductive fillers such as boron nitride were added inthe form of powders, and thus it was necessary to increase the fillingamount of the thermoconductive fillers up to approximately 60% byvolume. However, such technique would raise the cost, and the thermalconductivity of the heat dissipating member was 6 W/(m·K) or lower,resulting in difficulty in meeting the recent demands for higher thermalconductivity.

In the electronic parts using the heat dissipating member, when the heatdissipating member is a conventional one having large anisotropy inthermal conductivity, the arrangement of the cooling unit and the heattransport unit would be limited, thereby resulting in cases wherefurther miniaturization of the electronic device becomes difficult.Accordingly, development of a dissipating member having superior thermalconductivity and small anisotropy in the thermal conductivity isstrongly desired.

Regarding these problems, a heat dissipating member having superiorthermal conductivity and small anisotropy in the thermal conductivitycan be manufactured by using a resin-impregnated boron nitride sinteredbody containing a resin. Here, in the boron nitride sintered body,flake-like boron nitride particles having a specific calcium contentratio, specific graphitization index of the boron nitride, and suitablycontrolled average grain size are allowed to have a three-dimensionalbonding with small orientation degree in the boron nitride crystals,thereby enhancing the accessibility among the boron nitride particles.However, there has been no technical suggestion provided in these pointsof views.

CITATION LIST Patent Literature

[Patent Literature 1] JP 2002-212309A

[Patent Literature 2] JP 2010-275149A

[Patent Literature 3] JP 2008-248048A

[Patent Literature 4] JP H5-291706A

[Patent Literature 5] JP H6-152086A

[Patent Literature 6] JP 2010-153538A

[Patent Literature 7] JP H5-82760B

[Patent Literature 8] JP 2011-20444A

[Patent Literature 9] JP H9-202663A

[Patent Literature 10] JP 2009-263147A

[Patent Literature 11] WO2010/047278

SUMMARY OF INVENTION Technical Problem

(First Viewpoint)

However, although the method of Patent Literature 1 improves abrasionresistance and electric insulation by impregnating the resin into themolding having ceramics and metal contacting each otherthree-dimensionally, improvement in thermal conductivity was notsufficient.

In Patent Literature 2, a ceramics member as a sintered body containingat least one of forsterite and boron nitride as the main component, andhaving the boron nitride aligned in one direction; a probe holder formedby using the ceramics member; and a manufacturing method of the ceramicsmember are suggested. Here, a ceramics member having free-cuttingproperty as well as thermal expansion coefficient close to that ofsilicone, and high strength is suggested, however, improvement in thethermal conductivity was not sufficient.

In the method of Patent Literature 3, thermal conductivity was low asshowing a maximum value of 5.8 W/(m·K). In addition, the thermosettingresin needs to be crushed after being obtained, and then thethermosetting resin is mixed and softened again. Accordingly, it wasproblematic in the viewpoint of reliability due to the possibility ofcontamination and uniformity of the softening condition of the resin.

In the methods of Patent Literatures 4 and 5, there is no disclosureregarding the impregnation of the resin into the boron nitride sinteredbody simple substance, and thus the bending strength is as low as 28MPa, even though the maximum thermal conductivity is 45 W/(m·K).Therefore, it is difficult realize high thermal conductivity and highstrength.

In Patent Literature 6, the thickness of the sheet was 100 μm or less,and thus there was a problem in the viewpoint of reliability due to theuniformity of the softening condition of the resin and the boron nitridein the moisture-resistant condition.

In the conventional technique, the heat dissipating member ismanufactured via a mixing process to mix the ceramics powder such asboron nitride and the resin, an extrusion molding process, a coatingprocess, a heating process and the like. Therefore, it is difficult toobtain a structure having the boron nitride crystals contacting witheach other three-dimensionally. Accordingly, there was a limit in theimprovement in the thermal conductivity. In addition, even whenspherical particles of aluminum oxide powders and silicon oxide powdersare used, thermal conductivity of these ceramics powders isapproximately 20 to 30 W/(m·K) and is lower than that of boron nitride.Further, since the particles are hard, there was a problem in that theapparatus and the mold would be worn down. In addition, in the heatdissipating member manufactured by the conventional technique, thefilling amount of the ceramics powder such as the boron nitride needs tobe increased up to approximately 60 mass % in order to increase thethermal conductivity, however, since such technique would increase thecost, it was difficult to achieve both of low cost and superior propertywith the heat dissipating member. Here, a method for manufacturing acircuit substrate having superior workability and strength by allowing aresin to impregnate in a ceramics of which crystal grains are bonded ina three-dimensional network structure and has open pores, isconventionally known. However, although there is a disclosure that boronnitride and the like is added to provide thermal conductivity, it wasdifficult to realize high thermal conductivity and bending strength.

Regarding these problems, the present invention places importance in theheat dissipating property, and improves thermal conductivity andstrength by obtaining a composite material. Specifically, the inner gapof the boron nitride sintered body is impregnated with a resin, and thenthe impregnated boron nitride sintered body is cut into plates tomanufacture the heat dissipating member. Accordingly, the alignment canbe controlled in an arbitrary direction, and a heat dissipating memberhaving superior thermal conductivity with arbitrary thickness can bemanufactured easily. Therefore, a heat dissipating member which canobtain high reliability with respect to moisture and thermal cycle canbe manufactured. In addition, even when the filling amount of the boronnitride is relatively small, the structure having the boron nitridecontacting with each other three-dimensionally allows manufacture of aheat dissipating member having superior thermal conductivity. However,there has been no technical suggestion provided in these points ofviews.

The present invention provides a heat dissipating member having superiorthermal conductivity and strength, which is suitably used as a heatdissipating member of exothermic electronic parts such as power devicesand the like, especially used for insulating layer of a printed-wiringboard, thermal interface materials and double-side heat dissipatingpower modules for automobiles.

(Second Viewpoint)

The present invention provides a resin-impregnated boron nitridesintered body having superior thermal conductivity and small anisotropyof thermal conductivity, which is suitably used as a heat dissipatingmember of exothermic electronic parts such as power devices and thelike, especially used for insulating layer of a printed-wiring board,thermal interface materials, substrates for power modules, anddouble-side heat dissipating power modules for automobiles.

Solution to Problem

The afore-mentioned problems can be solved by at least one of the firstand the second viewpoints of the present invention described below. Thefeatures described for the first and the second viewpoints can becombined with each other, and such combination can achieve furthersuperior effects. The object and the effect of the first viewpoint canbe achieved by the feature of the first viewpoint of the presentinvention, and the object and the effect of the second viewpoint can beachieved by the feature of the second viewpoint of the presentinvention.

(First Viewpoint)

In order to solve the afore-mentioned problems, the present inventionadopts the following measures.

(1) A resin-impregnated boron nitride sintered body, comprising: 30 to90 volume % of a boron nitride sintered body having boron nitrideparticles bonded three-dimensionally; and 10 to 70 volume % of a resin;wherein the boron nitride sintered body has a porosity of 10 to 70%; theboron nitride particles of the boron nitride sintered body has anaverage long diameter of 10 μm or more; the boron nitride sintered bodyhas a graphitization index (GI) by powder X-ray diffractometry is 4.0 orless; and an orientation degree of the boron nitride particles of theboron nitride sintered body by I.O.P (The Index of OrientationPerformance) provided by the following equation is 0.01 to 0.05 or 20 to100.

I.O.P. is calculated from an intensity ratio of (100) diffraction linewith respect to (002) diffraction line measured from a directionparallel to a height direction of the boron nitride sintered body and anintensity ratio of (100) diffraction line with respect to (002)diffraction line measured from a direction perpendicular to the heightdirection of the sintered body, using the following equation.I.O.P=(I100/I002)par./(I100/I002)prep.

(2) The resin-impregnated boron nitride sintered body of (1), wherein ashore hardness measured with respect to the height direction of theresin-impregnated boron nitride sintered body is 25 HS or lower.

(3) The resin-impregnated boron nitride sintered body of (1) or (2),wherein: a 100 plane (a-axis) of the boron nitride particle is alignedwith respect to the height direction of the boron nitride sintered bodyhaving boron nitride particles bonded three-dimensionally; a three-pointbending strength measured with respect to the height direction of theboron nitride sintered body is 3 to 15 MPa; and a thermal conductivitymeasured from the height direction of the boron nitride sintered body is40 to 110 W/(m·K).

(4) The resin-impregnated boron nitride sintered body of (1) or (2),wherein: a 002 plane (c-axis) of the boron nitride particle is alignedwith respect to the height direction of the boron nitride sintered bodyhaving boron nitride particles bonded three-dimensionally; a three-pointbending strength measured with respect to the height direction of theboron nitride sintered body is 10 to 40 MPa; and a thermal conductivitymeasured from the height direction of the boron nitride sintered body is10 to 40 W/(m·K).

(Second Viewpoint)

In order to solve the afore-mentioned problems, the present inventionadopts the following measures.

(5) A resin-impregnated boron nitride sintered body, comprising: 30 to90 volume % of a boron nitride sintered body having boron nitrideparticles bonded three-dimensionally; and 10 to 70 volume % of a resin;wherein: the boron nitride sintered body has a calcium content of 500 to5000 ppm; the boron nitride sintered body has a graphitization index(GI) by powder X-ray diffractometry of 0.8 to 4.0; the boron nitridesintered body comprises flake-like boron nitride particles having anaverage long diameter of 10 μm or more; and an orientation degree byI.O.P (The Index of Orientation Performance) provided by the followingequation is 0.6 to 1.4, the orientation degree obtained from anintensity ratio of (100) diffraction line with respect to (002)diffraction line measured from a direction parallel to a heightdirection of the boron nitride sintered body and an intensity ratio of(100) diffraction line with respect to (002) diffraction line measuredfrom a direction perpendicular to the height direction of the sinteredbody, using the following equation.I.O.P=(I100/I002)par./(I100/I002)prep.

(6) The resin-impregnated boron nitride sintered body of (5), wherein:the boron nitride sintered body having the boron nitride particlesbonded three-dimensionally has a three-point bending strength of 5 to 40MPa, a thermal conductivity of 5 W/(m·K) or more, and a total porosityof 70% or less.

(Common Items)

(7) The resin-impregnated boron nitride sintered body of any one of (1)to (6), wherein the resin is a thermosetting resin.

(8) A heat dissipating member using the resin-impregnated boron nitridesintered body of any one of (1) to (7).

(9) A substrate for power module using the heat dissipating member of(8).

(10) A double-side heat dissipating power module for automobiles usingthe heat dissipating member of (8).

Advantageous Effects of Invention

From the first viewpoint of the present invention, the effect ofobtaining a heat dissipating member having superior thermal conductivityand strength can be achieved.

From the second viewpoint of the present invention, the effect ofobtaining a heat dissipating member using a resin-impregnated boronnitride sintered body having superior thermal conductivity and smallanisotropy of thermal conductivity can be achieved.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described. Thefirst and the second viewpoints are explained separately, however, anembodiment having the features of both of the first and the secondviewpoints can be realized. In the following explanation, the commonfeatures of the first and the second viewpoints will be explained in thefirst viewpoint, and the explanation will not be repeated in the secondviewpoint. Accordingly, the features explained in the first viewpointcan be applied to the second viewpoint, unless it deviate the spiritthereof.

In the present invention, “boron nitride particles” is defined as theprimary particles of boron nitride, “boron nitride sintered body” isdefined as a condition in which two or more of the primary particles arebonded by sintering, “resin-impregnated boron nitride sintered body” isdefined as a composite comprising the boron nitride sintered body and aresin, and “boron nitride molded body” is defined as the mold obtainedby calcifying the resin of the resin-impregnated boron nitride sinteredbody. The boron nitride molded body can be obtained by calcifying theresin component by calcinating the resin-impregnated boron nitridesintered body in the atmosphere at 650 to 1000° C. for 1 hour. The bondformed by the sinteration can be evaluated by observing the bondedportion between the primary particles at the cross-section of the boronnitride particles using a scanning type electronic microscope (forexample, “JSM-6010LA” (available from JEOL Ltd.)). As a preliminarytreatment before the observation, the boron nitride particles wereembedded in a resin, followed by processing by CP (cross sectionpolisher) method. Then, the particles were fixed on a sample stage,followed by osmium coating. Observation was carried out with amagnification of 1000 or 1500.

(First Viewpoint)

The heat dissipating member using the resin-impregnated boron nitridesintered body according to the first viewpoint of the present inventionhas an orientation degree shown by a specific I.O.P (The Index ofOrientation Performance), and is obtained by impregnating a specificamount of resin into a boron nitride sintered body, the boron nitrideparticle of the boron nitride sintered body having a controlled averagelong diameter. Accordingly, the heat dissipating member having superiorthermal conductivity and strength which cannot be realized by theconventional technique can be realized.

The boron nitride sintered body according to the first viewpoint of thepresent invention has an orientation degree represented by I.O.P (TheIndex of Orientation Performance) of 0.01 to 0.05 or 20 to 100, agraphitization index (GI) obtained by the powder X-ray diffractionmethod of 4.0 or lower, and a porosity of 10 to 70%. In addition, theboron nitride sintered body is structured with a boron nitride having athree-dimensionally bonded boron nitride particles with an average longdiameter of 10 μm or more. The boron nitride sintered body designed assuch did not exist to date, and is a very important factor to retainhigh thermal conductivity and high strength.

In addition, controlling of the shore hardness of the resin-impregnatedboron nitride sintered body to 25 HS or lower allows achievement ofsuperior toughness and decrease in the thermal resistance without usinggrease even under loaded environment.

The major difference compared with the conventional technique is thatthe resin-impregnated boron nitride sintered body according to the firstviewpoint of the present invention is structured with a boron nitridesintered body obtained as boron nitride particles bondedthree-dimensionally by sintering. The three-dimensional bonding is not asimple contact which can be observed by SEM and the like, but can beevaluated by measuring the three-point bending strength and the thermalconductivity of the boron nitride molded body obtained by calcifying theresin component of the resin-impregnated boron nitride sintered body. Inthe conventional resin-impregnated boron nitride sintered bodymanufactured by mixing the boron nitride powder and the resin, thethree-dimensional bond among the boron nitride is weak, and thus theboron nitride remaining after calcifying would be powdered and cannotmaintain a shape, or cannot satisfy the required properties of thethree-point bending strength and the thermal conductivity even when theshape is maintained.

<Average Long Diameter>

The average long diameter of the boron nitride particles in the boronnitride sintered body of the present invention is 10 μm or more. Whenthe average long diameter is less than 10 μm, the pore size of the boronnitride sintered body would become small, resulting in incompleteimpregnation of the resin. Accordingly, although the strength of theboron nitride sintered body itself can be improved, the effect ofimproving the strength by the resin would become small, and the strengthas the resin-impregnated boron nitride sintered body would decrease. Inaddition, the number of contacting points among the flake-like boronnitride particles would increase, thereby resulting in decrease in thethermal conductivity of the resin-impregnated boron nitride sinteredbody. There is no particular limitation regarding the upper limit of theaverage long diameter. Since it is difficult for the flake-like boronnitride particles to have an average long diameter of 50 μm or more,upper limit of the average long diameter is approximately 50 μm inreality.

<Definition and Evaluation Method of Average Long Diameter>

The average long diameter can be measured in the following manner. As apreliminary treatment before the observation, the boron nitride sinteredbody is embedded in a resin, followed by processing by CP (cross sectionpolisher) method. Then, the boron nitride sintered body was fixed on asample stage, followed by osmium coating. Then, SEM image is taken witha scanning type electronic microscope (for example, “JSM-6010LA”(available from JEOL Ltd.)), and the image of the particles at the crosssection is imported into an image analysis software, for example “A-ZOKUN” (available from Asahi Kasei Engineering Corporation) or “Mac-ViewVer. 4.0” (available from Mountech Co., Ltd.). The magnification of theimage was 1000, and the pixel number of image analysis was 1510×10⁴pixel. Long diameter was manually measured for arbitrary 100 particlesobtained, and the average value was taken as the average long diameter.

Measurement was conducted with the boron nitride molded body in asimilar manner.

<Porosity and Evaluation Method Thereof>

From the viewpoint of electric insulation and thermal conductivity ofthe resin-impregnated boron nitride sintered body, it is preferable thatboron nitride particles are contained by 30 to 90 volume % and the boronnitride particles have a three-dimensional bonding structure in theboron nitride sintered body of the present invention. Porosity ispreferably 70% or lower, more preferably 50% or lower. The porosity insuch range is preferable for improving the thermal conductivity of theresin-impregnated boron nitride sintered body. In addition, in order toimprove strength sufficiently by resin impregnation, the porosity ispreferably 10% or higher. Measurement of the porosity of the boronnitride sintered body can be obtained by the following equation from thebulk density (D) obtained from the size and mass of the boron nitridesintered body and theoretical density of the boron nitride (2.28 g/cm³).Measurement for the boron nitride molded body was conducted in a similarmanner.bulk density(D)=mass/volumeporosity of boron nitride sintered body=1−(D/2.28)

Porosity can be adjusted by the pressure applied when an isotropicpressure is applied to the boron nitrides intered body.

<Orientation Degree>

In the boron nitride sintered body of the first viewpoint of the presentinvention, the orientation degree represented by I.O.P (The Index ofOrientation Performance) is in the range of 0.01 to 0.05 or 20 to 100.When I.O.P. is out of the range of 0.01 to 0.05 or 20 to 100, the boronnitride crystals in the boron nitride sintered body is in the state ofnon-aligned condition. Accordingly, the anisotropy of the thermalconductivity would become small and it would become difficult to obtainsuperior thermal conductivity in the arbitrary direction with theresin-impregnated boron nitride sintered body. Orientation degree can becontrolled by the formulation amount of the amorphous boron nitridepowder and the hexagonal boron nitride powder particles as the rawmaterial or by the molding method.

<Definition of Orientation Degree and Evaluation Method Thereof>

I.O.P. of the boron nitride crystal can be calculated from the intensityratio of (100) diffraction line with respect to (002) diffraction linemeasured from a direction parallel to the height direction of the boronnitride sintered body and the intensity ratio of (100) diffraction linewith respect to (002) diffraction line measured from a directionperpendicular to the height direction of the boron nitride sinteredbody, using the following equation.I.O.P=(I100/I002)par./(I100/I002)prep.

When I.O.P=1 is satisfied, it means that the direction of the boronnitride crystals in the sample is random. The value of I.O.P. beingsmaller than 1 indicates that the (100) plane of the boron nitridecrystal in the boron nitride sintered body, that is, the a-axis of theboron nitride crystal is aligned parallel with the height direction. Onthe other hand, the value of I.O.P. exceeding 1 indicates that the (100)plane of the boron nitride crystal in the boron nitride sintered body,that is, the a-axis of the boron nitride crystal is alignedperpendicularly with the height direction. Measurement of I.O.P can beconducted by using “D8ADVANCE Super Speed” (available from Bruker AXSK.K.) for example. Measurement was conducted using CuKα ray as the X-raysource, the X-ray tube voltage was 45 kV, and the X-ray tube current was360 mA.

Measurement was conducted with the boron nitride molded body in asimilar manner.

<Graphitization Index (GI)>

Graphitization index (GI) can be obtained from the following equationusing the integrated intensity ratio, that is, the area ratio of (100)plane, (101) plane, and (102) plane of the X-ray diffraction diagram {J.Thomas, et. al, J. Am. Chem. Soc. 64, 4619 (1962)}.GI=[area{(100)+(101)}]/[area(102)]

Here, it is generally known that GI of fully crystallized boron nitrideis 1.60. In the case of a flake-like hexagonal boron nitride powderhaving high crystallinity with sufficiently grown particles, GI becomesmore smaller since the particles tend to align. That is, GI is an indexof the crystallinity of the flake-like hexagonal boron nitride powder,and the smaller the value, the higher the crystallinity. In the boronnitride molded body of the present invention, GI is preferably 4.0 orlower. The value of GI being higher than 4.0 indicates that thecrystallinity of the boron nitride primary particle is low, and thus thethermal conductivity of the boron nitride sintered body decreases. Here,when it is necessary to decrease the anisotropy of thermal conductivity,GI is preferably 0.8 or higher. The value of GI being lower than 0.8indicates that the crystallinity of the boron nitride primary particleis high. Since the flake-like shape of the boron nitride primaryparticle is excessively developed, the anisotropy of thermalconductivity with respect to the resin-impregnated boron nitridesintered body becomes large. GI can be controlled by the formulationamount of the hexagonal boron nitride powder particles as the rawmaterial, addition amount of calcium compound, and calcinationtemperature.

<Evaluation Method of Graphitization Index (GI)>

Measurement of GI can be conducted by using “D8ADVANCE Super Speed”(available from Bruker AXS K.K.) for example. As a preliminary treatmentbefore the measurement, the boron nitride sintered body is crushed usingan agate mortar, and then the boron nitride powder thus obtained wassubjected to press molding. X-ray was irradiated symmetrically withrespect to the normal vector of the plane in the in-plane direction ofthe mold. Measurement was conducted with CuKα ray as the X-ray source,the X-ray tube voltage was 45 kV, and the X-ray tube current was 360 mA.

Measurement was conducted with the boron nitride molded body in asimilar manner.

<Bending Strength>

Three-point bending strength was used as the strength of the boronnitride sintered body structuring the resin-impregnated boron nitridesintered body of the present invention. The three-point bending strengthis preferably 3 to 40 MPa, and more preferably 5 to 40 MPa. When thethree-point bending strength is lower than 3 MPa or 5 MPa, thethree-dimensional bonding area among the boron nitride particles wouldbe small, and the thermal conductivity of the resin-impregnated boronnitride sintered body becomes low as a result. In addition, it can causedestruction of the heat dissipating material when mounted, resulting indecrease in the electric insulation and decrease in reliability. On theother hand, the three-point bending strength being higher than 40 MPaindicates that the bonding area among the boron nitride particles islarge, and thus the porosity of the boron nitride sintered bodydecreases. Accordingly, it becomes difficult to impregnate the resinfully into the boron nitride sintered body, resulting in decrease in thestrength and in the electric insulation of the resin-impregnated boronnitride sintered body. Bending strength can be adjusted by the additionamount of calcium compound, calcination temperature when the boronnitride sintered body is prepared, and the pressure when isotropicpressure is applied.

When the 100 plane (a-axis) of the boron nitride particle is alignedwith respect to the height direction of the boron nitride sintered body,it is further preferable that the bending strength measured from theheight direction of the boron nitride sintered body is 3 to 15 MPa.Here, it is preferable that the thermal conductivity in the heightdirection is 40 to 110 W/(m·K). When the 002 plane (c-axis) of the boronnitride particle is aligned with respect to the height direction of theboron nitride sintered body, it is further preferable that the bendingstrength measured from the height direction of the boron nitridesintered body is 10 to 40 MPa. Here, it is preferable that the thermalconductivity in the height direction is 10 to 40 W/(m·K).

<Evaluation Method of Bending Strength>

The bending strength of the boron nitride sintered body was measuredunder the conditions defined in JIS-R1601 at room temperature (25° C.).Here, “autograph AG2000D” available from Shimadzu Corporation was used.Measurement was conducted with the resin-impregnated boron nitridesintered body and the boron nitride molded body in a similar manner.

<Dielectric Breakdown Strength and Evaluation Method Thereof>

The dielectric breakdown strength of the resin-impregnated boron nitridesintered body of the present invention is preferably 15 kV/ram orhigher. When the dielectric breakdown strength is lower than 15 kV/ram,electric insulation sufficient to be used as the heat dissipating membercannot be achieved, which is unfavorable. Measurement of the dielectricbreakdown strength can be conducted by using “AC compression testerITS-60005 (available from Tokyo-seiden.co.jp)”. The measurement can beconducted in accordance with JIS-C2141, by processing the measurementsamples to have a width of 50 mm, length of 50 mm, and thickness of 1.0mm; in an insulating oil under room temperature (25° C.) with anelectrode size of 025 mm.

<Thermal Conductivity>

Regarding the boron nitride sintered body structuring theresin-impregnated boron nitride sintered body of the present invention,the thermal conductivity is preferably 10 W/(m·K) or more. The thermalconductivity being less than 10 W/(m·K) indicates that thethree-dimensional bonding strength of the flake-like boron nitrideparticles is weak, and thus the thermal conductivity of theresin-impregnated boron nitride sintered body decreases. Thermalconductivity can be adjusted by the addition amount of calcium compound,calcination temperature when the boron nitride sintered body isprepared, and the pressure when the boron nitride sintered body isapplied with an isotropic pressure.

<Measuring Method of Thermal Conductivity>

Thermal conductivity (H: W/(m·K)) of boron nitride sintered body, boronnitride molded body and resin-impregnated boron nitride sintered bodywas calculated from thermal diffusivity (A: m²/sec), density (B: kg/m³),and specific heat capacity (C: J/(kg·K)), by the equation of H=A×B×C.Thermal diffusivity was obtained by the laser flash method with ameasuring sample processed to have a width of 10 mm, length of 10 mm,and thickness of 1.0 mm. As the measuring apparatus, xenon flashanalyzer (“LFA447 Nano Flash” available from NETZSCH Japan K.K.) wasused. Density was obtained using the Archimedes method. Specific heatcapacity was obtained using DSC (“ThermoPlus Evo DSC 8230” availablefrom Rigaku Corporation).

<Shore Hardness and Evaluation Method Thereof>

Shore hardness of the resin-impregnated boron nitride sintered body ofthe present invention is preferably 25 HS or lower. When the shorehardness exceeds the value of 25 HS, the resin-impregnated boron nitridesintered body would become brittle, and thus the stress applied bytightening and pinching when the resin-impregnated boron nitridesintered body is mounted as the heat dissipating member would causebreak in the resin-impregnated boron nitride sintered body. In addition,insufficient flexibility would increase the interface resistance,resulting in increase in the thermal resistance. Measurement of theshore hardness can be conducted by using, for example, “shore D hardnessmeter, available from Shimadzu Corporation”. Measurement was conductedwith the boron nitride sintered body and boron nitride molded body in asimilar manner.

<Thermal Resistance and Evaluation Method Thereof>

When the resin-impregnated boron nitride sintered body is used as theheat dissipating member, the thermal resistance is preferably as smallas possible. When the interface thermal resistance is large, the thermalconductivity calculated from the laser flash method and the likedeviates largely from the thermal resistance when mounted. Here, thevalue of the thermal conductivity when mounted would become low.Further, regarding the grease applied to the interface with thesubstrate to relieve the interface thermal resistance, the amount of thegrease, which decreases the thermal conductivity, can be suppressed byusing a resin-impregnated boron nitride sintered body having low shorehardness and low interface thermal resistance. Measurement of thethermal resistance of the resin-impregnated boron nitride sintered bodycan be conducted in accordance with ASTM-D5470, and the value of thethermal resistance in the present measurement is a value including thethermal resistance of the bulk and the interface thermal resistance atthe contacting plane. The size of the samples were 10 mm×10 mm,thickness was 0.3 mm, applied load was 9.8 kgf/cm³, and the measurementwas conducted greaseless.

<Purity of Boron Nitride and Evaluation Method Thereof>

In addition, the purity of boron nitride in the boron nitride sinteredbody and boron nitride model of the present invention is preferably 95mass % or higher. The purity of boron nitride can be measured byalkalinolysis of the boron nitride powder, followed by steamdistillation using Kjeldahl method, and then measurement of all ofnitrogen contained in the distillate by neutralization titration.

<Definition of Average Grain Size of Boron Nitride Powder and EvaluationMethod Thereof>

The average grain size of the boron nitride powder used as the startingmaterial of the boron nitride sintered body is the grain size ofaccumulated value of 50% for accumulated particle distribution obtainedin the particle size distribution measurement by the laser diffractionscattering method. As the size distribution measuring apparatus,“MT3300EX” (available from NIKKISO CO., LTD.) can be used. When themeasurement was conducted, water was used as the solvent,hexametaphosphoric acid was used as the dispersant, and the boronnitride powder was dispersed using a homogenizer at 20 W output for 30minutes as pretreatment. The refractive index of the water was taken as1.33, and the refractive index of the boron nitride powder was taken as1.80. The measurement period for one measurement was 30 seconds.

<Sintering Conditions of Boron Nitride Sintered Body>

The boron nitride sintered body of the present invention is manufacturedpreferably by preparing a spherical boron nitride powder byspheroidizing the slurry containing the boron nitride powder using aspray dryer and the like, and then filling the spherical boron nitridepowder into a container of boron nitride and the like, followed bysintering at 1600° C. or higher for 1 hour or longer. When the sinteringis not conducted, the pore size would be small, and it would bedifficult to impregnate the resin. It is important to manufacture theboron nitride sintered body by conducting calcination at 1600° C. orhigher for 1 hour or longer, in order to obtain the boron nitridesintered body having I.O.P. in a particular range. When the sinteringtemperature is lower than 1600° C., the crystallinity of the boronnitride would not be improved sufficiently, and thus the thermalconductivity of the resin-impregnated boron nitride sintered body maydecrease. Although there is no particular limitation regarding the upperlimit of the sintering temperature, an upper limit of approximately2200° C. is practical, in economic terms of view. In addition, when thesintering period is shorter than 1 hour, the crystallinity of the boronnitride would not be improved sufficiently, and thus the thermalconductivity of the boron nitride sintered body may decrease. Althoughthere is no particular limitation regarding the upper limit of thesintering period, an upper limit of approximately 30 hours is practical,in economic terms of view. In addition, sintering is preferablyconducted under nitrogen or argon atmosphere in order to preventoxidation of the boron nitride sintered body.

<Programming Rate During Manufacture of Boron Nitride Sintered Body>

In the sintering process of the boron nitride sintered body of thepresent invention, it is preferable that the programming rate in thetemperature range of 300 to 600° C. is 40° C./min or lower. When theprogramming rate is higher than 40° C./min, rapid decomposition of theorganic binder would cause a distribution in the sintering property ofthe boron nitride particles, thereby resulting in large variation in theproperties and decrease in reliability. Although there is no particularlimitation regarding the lower limit of the programming rate, a lowerlimit of approximately 5° C./min is practical, in economic terms ofview.

<Heat Dissipating Member>

The heat dissipating member using the resin-impregnated boron nitridesintered body of the present invention is described. The heatdissipating member of the present invention is obtained in the followingmanner. Resin is impregnated in the boron nitride sintered body,followed by curing, thereby obtaining the resin-impregnated boronnitride sintered body. Subsequently, using a multi wire saw and thelike, the resin-impregnated boron nitride sintered body is cut into aplate-shaped resin-impregnated boron nitride sintered body havingarbitrary thickness. The plate-shaped resin-impregnated boron nitridesintered body is suitably used to manufacture the heat dissipatingmember of the present invention. By using a processing apparatus such asthe multi wire saw and the like, the resin-impregnated boron nitridesintered body can be cut out with arbitrary thickness by mass amount,and the surface roughness after cutting would show a favorable value. Inaddition, by altering the direction of the resin-impregnated boronnitride sintered body when the cutting is conducted, a plate-shapedresin-impregnated boron nitride sintered body having superior thermalconductivity with respect to an arbitrary direction can be easilyobtained.

<Increasing Density of Boron Nitride Sintered Body>

The boron nitride sintered body of the present invention ischaracteristic in that it is manufactured via a densification process byapplying an isotropic pressure in order to improve the adhesion propertyof the flake-like boron nitride particles to improve the thermalconductivity. As the method for applying pressure, applying coldisotropic pressure using a CIP (cold isotropic pressing) machine can bementioned for example. The boron nitride sintered body is sealed in aplastic bag and placed in a rubber mold, followed by application ofpressure using the CIP machine. Preferable pressure is 1 to 300 MPa.

<Composite with Resin>

Next, the method for obtaining a composite of boron nitride sinteredbody and resin will be explained. The resin-impregnated boron nitridesintered body of the present invention is suitably manufactured byimpregnating a resin in the boron nitride sintered body followed bycuring. The resin can be impregnated by vacuum impregnating, pressurizedimpregnating at 1 to 300 MPa (preferably 3 to 300 MPa), heatedimpregnating at r.t. to 150° C., or combination thereof. The pressureduring the vacuum impregnating is preferably 1000 Pa or lower, and morepreferably 50 Pa or lower. With respect to pressurized impregnating, theresin would not sufficiently impregnate into the boron nitride sinteredbody when the pressure is lower than 1 MPa. On the other hand, when thepressure is 300 MPa or higher, the facility would become large, raisingthe cost. By decreasing the viscosity of the resin, the resin can beimpregnated into the boron nitride sintered body. Therefore, it isfurther preferable to increase the temperature to a temperature range of30 to 300° C. and to decrease the viscosity of the resin when pressureis applied.

<Resin>

As the resin, epoxy resin, silicone resin, silicone rubber, acrylicresin, phenol resin, melamine resin, urea resin, unsaturated polyester,fluorine resin, polyamide such as polyimide, polyamide imide, polyetherimide and the like, polyester such as polybutylene terephthalate,polyethylene terephthalate and the like, polyphenylene ether,polyphenylene sulfide, fully aromatic polyester, polysulfone, liquidcrystal polymer, polyether sulfone, polycarbonate, modified maleimideresin, ABS resin, AAS (acrylonitrile-acryl rubber⋅styrene) resin, AES(acrylonitrile⋅ethylene⋅propylene⋅dine rubber-styrene) resin,polyglycolic acid resin, poly phthalimide, polyacetal and the like canbe used for example. In particular, epoxy resin is suitable for theinsulating layer of a printed-wiring board since its heat resistance andadhesion strength with respect to a copper foil circuit are superior. Inaddition, silicone resin is suitable as the thermal interface materialssince heat resistance, flexibility and adhesion property with respect toa heat sink and the like are superior. These resins, especiallythermosetting resin can contain curing agent, inorganic fillers, silanecoupling agent, and further an additive to enhance the improvement inthe wettability and leveling property and decrease in the viscosity,thereby decreasing occurrence of defects during hot-press molding. Asthe additive, for example, antifoaming agent, surface conditioner,wetting-and-dispersing agent and the like can be mentioned for example.In addition, it is further preferable that the resin contains one ormore types of a ceramics powder selected from the group consisting ofaluminum oxide, silicon oxide, zinc oxide, silicon nitride, aluminumnitride, and aluminum hydroxide. The ceramics powder can be filled inbetween the boron nitride particles, thereby allowing improvement of thethermal conductivity of the boron nitride resin mold. The resin and theceramics powder containing resin can be diluted with a solvent asnecessary. As the solvent, alcohols such as ethanol, isopropanol and thelike, ether alcohols such as 2-methoxyethanol, 1-methoxyethanol,2-ethoxyethanol, 1-ethoxy-2-propanol, 2-butoxyethanol,2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol,2-(2-butoxyethoxy)ethanol and the like, glycol ethers such as ethyleneglycol monomethyl ether, ethylene glycol monobutyl ether and the like,ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone anddi-isobutyl ketone, hydrocarbons such as toluene and xylene can bementioned for example. Here, these diluents can be used alone or two ormore types can be used in combination.

(Second Viewpoint)

The resin-impregnated boron nitride sintered body according to thesecond viewpoint of the present invention can obtain a heat dissipatingmember having superior thermal conductivity and small anisotropy ofthermal conductivity, which cannot be achieved by the conventionaltechnique, by using the resin-impregnated boron nitride sintered bodycontaining a boron nitride sintered body and a resin. Here, in the boronnitride sintered body, accessibility among the boron nitride particlesis enhanced by allowing the orientation degree of the boron nitridecrystals to be small and by further allowing the flake-like boronnitride particles to bond three-dimensionally. Here, the flake-likeboron nitride particles have specific calcium content and graphitizationindex of the boron nitride, and the average long diameter of theflake-like boron nitride is appropriately controlled.

The resin-impregnated boron nitride sintered body according to thesecond viewpoint of the present invention contains three-dimensionallybonded boron nitride sintered body by 30 to 90 volume %, and a resin by10 to 70 volume %, and comprises flake-like boron nitride particles ofwhich boron nitride sintered body has an average long diameter of 10 μmor more. In addition, the orientation degree represented by I.O.P. is0.6 to 1.4, the calcium content is 500 to 5000 ppm, and thegraphitization index obtained by the powder X-ray diffractometry is 0.8to 4.0. The resin-impregnated boron nitride sintered body designed assuch did not exist to date, and is a very important factor to retainhigh thermal conductivity and small anisotropy of thermal conductivitywhen used as a heat dissipating member.

The major difference compared with the conventional technique is thatthe resin-impregnated boron nitride sintered body according to thesecond viewpoint of the present invention is a boron nitride sinteredbody obtained by bonding boron nitride particles three-dimensionally bysintering. The meaning of the three-dimensional bonding is as explainedin the first viewpoint. In addition, since the orientation degree of theboron nitride crystal was large in the conventional technique, there wasa limit in decreasing the anisotropy of thermal conductivity.

<Orientation Degree>

In order to decrease the anisotropy of the thermal conductivity withrespect to the resin-impregnated boron nitride sintered body, it isnecessary to decrease the orientation degree of the boron nitridecrystals. Regarding the boron nitride sintered body structuring theresin-impregnated boron nitride sintered body, the orientation degreerepresented by I.O.P. is 0.6 to 1.4. When I.O.P. is out of the range of0.6 to 1.4, the boron nitride crystals are aligned in a specificdirection, and thus the anisotropy of the thermal conductivity withrespect to the resin-impregnated boron nitride sintered body becomeslarge. Orientation degree can be controlled by the formulation amount ofthe amorphous boron nitride powder and the hexagonal boron nitridepowder particles as the raw material. Here, in general, I.O.P. of theboron nitride sintered body manufactured by conventional technique is0.5 or lower and 2 or higher. The definitions of orientation degree andevaluation method thereof are as described in the first viewpoint.

<Content of Calcium and Evaluation Method Thereof>

In the resin-impregnated boron nitride sintered body according to thesecond viewpoint of the present invention, what is particularlyimportant is that the calcium content of the boron nitride sintered bodyis 500 to 5000 ppm. When the calcium content is less than 500 ppm, thesintering of the boron nitride would not proceed sufficiently and formsa powder, and thus cannot be taken as the sintered body. When thecalcium content is larger than 5000 ppm, the thermal conductivity of theresin-impregnated boron nitride sintered body would decrease. The rangeof the calcium content is more preferably 1000 to 4500 ppm. The calciumcontent can be measured by using a wavelength-dispersive X-rayfluorescence analysis device “ZSX Primus II (available from RigakuCorporation)” for example. As a preliminary treatment before themeasurement, the boron nitride sintered body is crushed using an agatemortar, and then the boron nitride powder thus obtained was pressmolded. When the measurement was conducted, Rh vacuum tube was used asthe X-ray tube, the electric power of the X-ray tube was 3.0 kW, andmeasuring diameter was Φ=30 mm. Measurement was conducted with the boronnitride molded body in a similar manner.

EXAMPLES

Hereinafter, the present invention will be described specifically withreference to Examples and Comparative Examples.

(First Viewpoint)

<Preparation of Boron Nitride Sintered Body>

Amorphous boron nitride powder (oxygen content of 1.5%, boron nitridepurity of 97.6%, average grain size of 6.0 μm) and hexagonal boronnitride powder (oxygen content of 0.3%, boron nitride purity of 99.0%,average grain size of 18.0 μm or 30.0 μm) were mixed using a Henschelmixer, to give a mixed powder. Subsequently, the mixed powder formolding was used to conduct press molding at 5 MPa to give a blockmolded body. The block molded body thus obtained was sintered in abatch-type high-frequency furnace with a nitrogen flow of 10 L/min,thereby obtaining a boron nitride sintered body. In some of theexperimental conditions, pressure treatment was performed with apressure ranging in 10 to 100 MPa, by a cold isotropic pressing method(CIP).

<Vacuum Impregnation of Epoxy Resin>

The resin was impregnated into the boron nitride sintered body thusobtained. A mixture of the boron nitride sintered body and epoxy resin(“bond E205” available from Konishi Co., Ltd) with an attached curingagent was degassed under vacuum of 50 Pa for 10 minutes, and was thenpoured into the boron nitride sintered body under vacuum, followed byimpregnation for 20 minutes. Subsequently, the resin was cured byheating at 150° C. for 60 minutes, thereby obtaining theresin-impregnated boron nitride sintered body.

<Preparation of Plate-Shaped Resin-Impregnated Boron Nitride SinteredBody>

To evaluate the properties of the resin-impregnated boron nitridesintered body obtained as the heat dissipating member, theresin-impregnated boron nitride sintered body was processed into anarbitrary shape using a multi wire saw or a machining center. Here, theresin-impregnated boron nitride sintered body was cut out so that the100 plane (a-axis) or the 002 plane (c-axis) would align with respect tothe thickness direction. In addition, the resin-impregnated boronnitride sintered body thus obtained was calcinated in air at 1000° C.for 1 hour, thereby calcifying the resin component to obtain the boronnitride molded body. The results of the evaluation for the boron nitridesintered body and the resin-impregnated boron nitride sintered body areshown in Table 1-1 to Table 1-2.

The boron nitride sintered body and the boron nitride molded body werethe same in the average long diameter of the boron nitride particles,alignment of the 100 plane (a-axis) or the 002 plane (c-axis) of theboron nitride particles with respect to the height direction, porosity,I.O.P., graphitization index by powder X-ray diffractometry, and shorehardness.

Here, regarding the boron nitride sintered body and the boron nitridemolded body, bending strength and thermal conductivity measured withrespect to the height direction when the 100 plane (a-axis) of the boronnitride particles were aligned with respect to the height direction; andbending strength and thermal conductivity measured with respect to theheight direction when the 002 plane (c-axis) of the boron nitrideparticles were aligned with respect to the height direction; were thesame.

TABLE 1-1 boron nitride sintered body thermal shore bending conductivityhardness in strength in graph- average CIP in height height heightsinter- align- itization diameter porosity pressure direction directiondirection condition ation ment LOP index (μm) (%) MPa W/(m · K) HS MPatype 1A conducted a-axis 0.042 1.1 20 33 100 93.2 9.0 8.8 Example 1Cconducted a-axis 0.023 1.1 18 61 20 55.8 6.5 4.9 Example 1G none a-axis0.039 4.2 10 67 10 8.0 11.0 9.1 Comparative Example 1I conducted a-axis0.042 1.1 20 91 0 not not not Comparative Example available availableavailable 1B conducted c-axis 23.81 1.1 20 33 100 30.2 11.0 27.4 Example1D conducted c-axis 42.00 1.1 18 52 20 20.5 8.0 12.2 Example 1Econducted c-axis 76.92 0.8 30 65 100 33.2 5.1 10.5 Example 1F conductedc-axis 32.26 3.7 12 15 100 13.5 10.2 39.8 Example 1H none c-axis 25.003.5 7 13 100 10.7 8.3 8.8 Comparative Example 1J conducted none 1.0002.2 22 70 0 9.5 7.0 10.0 Comparative Example

TABLE 1-2 resin-impregnated boron nitride sintered body boron thermalshore bending nitride conductivity hardness in strength in sintered inheight height height thermal body resin direction direction directionresistance condition volume % volume % W/(m · K) HS MPa ° C./W Type 1A70% 30% 94.4 19.5 26.0 0.279 Example 1C 61% 49% 57.6 17.0 23.2 0.348Example 1G 90% 10% 8.3 11.0 9.3 1.364 Comparative Example 1I 10% 90% 1.040.0 40.0 3.474 Comparative Example 1B 76% 24% 31.9 19.3 66.3 0.376Example 1D 45% 55% 22.1 23.5 41.2 0.455 Example 1E 34% 66% 35.9 12.135.5 0.315 Example 1F 85% 15% 14.5 14.5 43.0 0.561 Example 1H 94%  6%10.9 9.0 9.1 0.781 Comparative Example 1J 19% 81% 10.5 35.0 22.0 1.785Comparative Example

As obvious from the comparison between the Examples and the ComparativeExamples, the heat dissipating member using the plate-shapedresin-impregnated boron nitride sintered body according to the firstviewpoint of the present invention has high thermal conductivity andhigh bending strength, thereby showing superior properties.

(Second Viewpoint)

<Preparation of Boron Nitride Sintered Body>

Amorphous boron nitride powder, hexagonal boron nitride powder, andcalcium carbonate (“PC-700” available from Shiraishi Kogyo Kaisha, Ltd.)were mixed using a Henschel mixer, followed by addition of water.Subsequently, the mixture was crushed using a ball mill for 5 hours togive an aqueous slurry. Then, to the aqueous slurry, polyvinyl alcoholresin (“Gohsenol” available from The Nippon Synthetic Chemical IndustryCo., Ltd.) was added by 0.5 mass %, followed by agitation with heatingat 50° C. until dissolved. Subsequently, spheroidizing treatment wascarried out at a drying temperature of 230° C. using a spray dryer.Here, as the spheroidizing apparatus of the spray dryer, rotary atomizerwas used. The resulting material thus obtained was filled in a boronnitride container, followed by atmospheric pressure sintering using abatch-type high-frequency furnace with a nitrogen flow of 5 L/min. Then,the sintered body was taken out from the boron nitride container toobtain the boron nitride sintered body. Subsequently, CIP was used topressurize the boron nitride sintered body under prescribed conditionsto conduct densification. As shown in Table 2-1, average grain size ofboron nitride powder, formulation ratio, spray drying conditions,calcination conditions, and CIP pressurizing conditions were adjusted toprepare 17 types of boron nitride sintered body.

TABLE 2-1 spray drying average diameter condition of boron nitriderotation powder (μm) formulation ratio (mass %) number of calcinationCIP amorphous hexagonal amorphous hexagonal atomizer temperaturepressure condition BN BN BN BN CaCO₃ water (rpm) (° C.) (MPa) 2A 10.117.50 7.50 0.47 74.53 9000 2000 10 2B 1.5 6.5 17.50 7.50 0.47 74.53 90002000 10 2C 3.4 10.1 12.75 2.25 0.64 84.36 9000 2100 10 2D 3.4 10.1 15.4012.60 0.52 71.48 9000 2000 10 2E 3.4 10.1 17.50 7.50 0.12 74.19 90002000 10 2F 3.4 10.1 17.60 7.50 0.81 74.63 9000 2000 10 2G 3.4 10.1 17.507.50 0.37 74.53 9000 1700 10 2H 3.4 10.1 17.60 7.50 0.47 74.53 9000 20005 2I 3.4 10.1 17.50 7.50 0.47 74.53 9000 2000 100 2J 1.1 3.2 17.50 7.500.47 74.53 9000 1700 10 2K 3.4 10.1 23.75 1.25 0.47 74.53 9000 2200 102L 3.4 10.1 3.30 29.70 0.62 66.38 9000 2000 10 2M 3.4 10.1 17.50 7.500.08 74.92 9000 2000 10 2N 3.4 10.1 17.50 7.50 1.12 73.88 9000 2000 102O 3.4 10.1 17.60 7.50 0.47 74.63 9000 1500 10 2P 3.4 10.1 5.00 20.001.12 73.88 9000 2200 500 2Q 3.4 10.1 17.50 7.50 0.47 74.53 9000 2000 CIPnot performed

Impregnation of Epoxy Resin, Examples 2-1 to 2-9 and ComparativeExamples 2-1 to 2-8

Resin impregnation was conducted with the boron nitride sintered bodythus obtained. A mixture of boron nitride sintered body, epoxy resin(“Epikote 807” available from Mitsubishi Chemical Corporation) andcuring agent (“Akumex H-84B” available from Nihon Gosei Kako Co., Ltd.)was degassed under vacuum of 50 Pa for 20 minutes, and then the epoxyresin mixture was poured into the boron nitride sintered body undervacuum, followed by 30 minutes of impregnation. Then, nitrogen gas wasused to pressurize with a pressure of 3 MPa at 120° C. for 30 minutes,thereby impregnating and curing the resin to obtain theresin-impregnated boron nitride sintered body.

Impregnation of Silicone Resin, Example 2-10

Boron nitride sintered body and silicone resin (“YE5822” available fromMomentive Performance Materials Inc.) were degassed under vacuum of 50Pa for 20 minutes, and then the silicone resin was poured into the boronnitride sintered body under vacuum, followed by 30 minutes ofimpregnation. Then, nitrogen gas was used to pressurize with a pressureof 3 MPa at 20° C. for 30 minutes, thereby impregnating the resin.Subsequently, the material was heated using a drying apparatus at 150°C. for 60 minutes to obtain the resin-impregnated boron nitride sinteredbody.

The resin-impregnated boron nitride sintered body thus obtained wascalcinated at 1000° C. for 1 hour under air, thereby calcifying theresin component to obtain the boron nitride molded body. The evaluationresults of the boron nitride sintered body and the resin-impregnatedboron nitride sintered body obtained for the Examples and ComparativeExamples are shown in Table 2-2 and Table 2-3. Here, when the sinteringof the boron nitride sintered body was insufficient and thus resulted ina powder, the boron nitride sintered body could not be taken out fromthe boron nitride container. In such case, the result was shown as“unable to take out due to powdering”.

Regarding the boron nitride sintered body and the boron nitride moldedbody, the average long diameter of the boron nitride particles,porosity, I.O.P., graphitization index by powder X-ray diffractometry,and calcium content were the same.

Here, regarding the boron nitride sintered body and the boron nitridemolded body, bending strength and thermal conductivity measured withrespect to the height direction when the 100 plane (a-axis) of the boronnitride particles were aligned with respect to the height direction; andbending strength and thermal conductivity measured with respect to theheight direction when the 002 plane (c-axis) of the boron nitrideparticles were aligned with respect to the height direction; were thesame.

TABLE 2-2 boron nitride sintered body average grain thermal size ofconductivity flame-like in boron nitride calcium total bending heightparticles content GI porosity strength direction condition (μm) I.O.P(ppm) (m) (%) (MPa) (W/mK) comments Example 2-1 2A 17 1.1 3860 1.6 46 1234 — Example 2-2 2B 11 1.0 2050 1.6 45 17 24 — Example 2-3 2C 20 0.71730 0.9 42 16 27 — Example 2-4 2D 16 1.4 1690 1.6 46 10 38 — Example2-5 2E 13 0.9 960 1.6 44 4 24 — Example 2-6 2F 17 0.8 4450 1.6 47 18 28— Example 2-7 2G 18 0.9 2210 3.7 43 3 22 — Example 2-8 2H 18 1.0 19401.6 51 10 27 — Example 2-9 2I 16 1.0 1910 1.6 30 35 46 — Example 2-10 2A17 1.1 1960 1.6 45 12 31 — Comparative 2J 5 0.9 2010 3.1 46 10 9 —Example 2-1 Comparative 2K 27 0.4 1240 0.7 45 22 9 — Example 2-2Comparative 2L 25 1.8 1610 1.8 44 7 41 — Example 2-3 Comparative 2M — —— — — — — unable to take out Example 2-4 due to powdering Comparative 2N37 1.2 5850 1.3 45 22 14 — Example 2-5 Comparative 2O 16 0.8 2340 4.5 433 4 — Example 2-6 Comparative 2P 26 0.5 5610 0.7 14 44 18 — Example 2-7Comparative 2Q 37 1.0 1990 2.0 73 6 11 — Example 2-8

TABLE 2-3 resin-impregnated boron nitride sintered body thermal thermalratio of boron conductivity conductivity thermal dielectric nitrideresin in height in planar conductivity breakdown (volume (volumedirection direction (height/ strength resin %) %) W/(m · K) W/(m · K)plane) kV/mm comments Example 2-1 epoxy 55 45 33 31 1.06 22 — Example2-2 epoxy 55 45 22 20 1.10 20 — Example 2-3 epoxy 58 42 25 31 0.81 20 —Example 2-4 epoxy 54 46 37 31 1.19 23 — Example 2-5 epoxy 66 44 24 260.92 24 — Example 2-6 epoxy 53 47 27 31 0.87 21 — Example 2-7 epoxy 5743 23 26 0.88 23 — Example 2-8 epoxy 38 61 28 27 1.04 23 — Example 2-9epoxy 70 30 44 46 0.96 16 — Example 2-10 sili- 55 46 30 27 1.11 26 —cone Comparative epoxy 64 46 8 10 0.80 23 — Example 2-1 Comparativeepoxy 55 45 8 34 0.24 21 — Example 2-2 Comparative epoxy 54 44 38 8 4.7520 — Example 2-3 Comparative epoxy 55 45 — — — — unable to take outExample 2-4 due to powdering Comparative epoxy 56 46 14 11 1.27 20 —Example 2-5 Comparative epoxy 55 43 4 6 0.67 26 — Example 2-6Comparative epoxy 88 14 16 41 0.39 11 — Example 2-7 Comparative epoxy 2773 11 10 1.10 25 — Example 2-8

As obvious from the comparison between the Examples and the ComparativeExamples, the heat dissipating member using the resin-impregnated boronnitride sintered body according to the second viewpoint of the presentinvention has high thermal conductivity and small anisotropy of thermalconductivity.

INDUSTRIAL APPLICABILITY

The heat dissipating member using the resin-impregnated boron nitridesintered body of the present invention can be suitably used as the heatdissipating member of the exothermic electronic parts such as powerdevices and the like. In particular, it can be used for the insulatinglayer and thermal interface materials of a printed-wiring board and forthe double-side heat dissipating power modules for automobiles.

The invention claimed is:
 1. A resin-impregnated boron nitride sinteredbody, comprising: 30 to 90 volume % of a boron nitride sintered bodyhaving hexagonal boron nitride particles bonded three-dimensionally; and10 to 70 volume % of a resin; wherein the boron nitride sintered bodyhas a porosity of 10 to 70%; the hexagonal boron nitride particles ofthe boron nitride sintered body has an average long diameter of 10 μm ormore; the boron nitride sintered body has a graphitization index (GI) bypowder X-ray diffractometry is 4.0 or less; the boron nitride sinteredbody is plate-shaped; and an a-axis of the hexagonal boron nitrideparticles is aligned with respect to a plate-thickness direction of theboron nitride sintered body.
 2. The resin-impregnated boron nitridesintered body of claim 1, wherein a shore hardness measured with respectto the plate-thickness direction of the resin-impregnated boron nitridesintered body is 25HS or lower.
 3. The resin-impregnated boron nitridesintered body of claim 1, wherein: a three-point bending strengthmeasured with respect to the plate-thickness direction of the boronnitride sintered body is 3 to 15 MPa; and a thermal conductivitymeasured from the plate-thickness direction of the boron nitridesintered body is 40 to 110 W/(m·K).
 4. The resin-impregnated boronnitride sintered body of claim 2, wherein: a three-point bendingstrength measured with respect to the plate-thickness direction of theboron nitride sintered body is 3 to 15 MPa; and a thermal conductivitymeasured from the plate-thickness direction of the boron nitridesintered body is 40 to 110 W/(m·K).
 5. The resin-impregnated boronnitride sintered body of claim 1, wherein the resin is a thermosettingresin.
 6. A heat dissipating member using the resin-impregnated boronnitride sintered body of claim
 1. 7. A substrate for power module usingthe heat dissipating member of claim
 6. 8. A double-side heatdissipating power module for automobiles using the heat dissipatingmember of claim 6.